Samal N.R.,City College of New York |
Owens E.M.,Upstate Freshwater Institute
Hydrological Processes | Year: 2013
The New York City water supply region, located in the Catskill Mountains in upstate New York, has always had a historically variable snow cover, with consequent effects on the magnitude of spring runoff and the relative importance of winter versus spring periods on annual hydrologic and nutrient budgets. Simulations show that under present conditions (1966-2005), on average 38% (12%-70%) of the annual total dissolved phosphorus load occurs during winter (Nov-Feb), while future predictions (2046-2065 and 2081-2100) show winter nutrient loads may account for an average of 46% (18%-73%) of the annual load. It is expected that changes in the importance of winter nutrient loading will lead to some increase in phytoplankton growth under isothermal conditions prior to the onset of thermal stratification, a reduced bloom coinciding with the onset of thermal stratification, and on an annual basis somewhat lower levels of biomass. However, future climate simulations using two different one-dimensional reservoir water quality models show no strong relationship between changes in algal biomass and the proportion of winter nutrient loading. The lack of a winter response calls into question model assumptions concerning the growth potential of phytoplankton under deeply mixed low light conditions, as well as factors influencing the bioavailability of nutrients input during the winter period. This illustrates the pitfalls of simulating future climate conditions, when the seasonality of model drivers has changed, and processes regulating winter conditions are not strongly represented. © 2013 John Wiley & Sons, Ltd.
Lee Z.,University of Massachusetts Boston |
Pahlevan N.,University of Massachusetts Boston |
Ahn Y.-H.,Korea Advanced Institute of Science and Technology |
O'Donnell D.,Upstate Freshwater Institute
Applied Optics | Year: 2013
It has been a long-standing goal to precisely measure water-leaving radiance (Lw, or its equivalent property, remote-sensing reflectance) in the field, but reaching this goal is quite a challenge. This is because conventional approaches do not provide a direct measurement of Lw, but rather measure various related components and subsequently derive this core property from these components. Due to many uncontrollable factors in the measurement procedure and imprecise post-measurement processing routines, the resulting Lw is inherently associated with various levels of uncertainties. Here we present a methodology called the skylight-blocked approach (SBA) to measure Lw directly in the field, along with results obtained recently in the Laurentian Great Lakes. These results indicate that SBA can measure Lw in high precision. In particular, there is no limitation of water types for the deployment of SBA, and the requirement of post-measurement processing is minimum; thus high-quality Lw for a wide range of aquatic environments can be acquired. © 2013 Optical Society of America.
Peng F.,Upstate Freshwater Institute |
Effler S.W.,Upstate Freshwater Institute
Journal of Great Lakes Research | Year: 2010
Light-scattering attributes of minerogenic particles from the water column of the western basin of Lake Erie (13 sites, plus one from the central basin and one from Sandusky Bay), collected after a wind event, were characterized by scanning electron microscopy interfaced with automated image and X-ray analyses (SAX). SAX results specified scattering attributes for individual particles, including size and chemical composition, and were used in forward Mie theory calculations of minerogenic scattering and backscattering coefficients (bm and bb,m). Clay mineral particles, in the size range of 1-20μm, were the dominant form of minerogenic scattering, representing >75% of bm and bb,m. Levels of bm and bb,m were high in the western basin, apparently in part due to wind-driven sediment resuspension, and wide spatial variability was observed. The credibility of the SAX-Mie estimates of bm and bb,m was supported by the extent of optical closure obtained with paired bulk measurements of particulate scattering and backscattering coefficients (bp and bbp), and independent estimates of organic particle contributions based on empirical bio-optical models. Minerogenic particles dominated bp and particularly bbp, and regulated spatial differences in the related common metrics of optical water quality, including turbidity and clarity. The bbp:bp ratio was found to be a good predictor of the spatial differences in the relative contributions of minerogenic particles versus phytoplankton to scattering. © 2010 International Association for Great Lakes Research.
Effler S.W.,Upstate Freshwater Institute |
Peng F.,Upstate Freshwater Institute
Fundamental and Applied Limnology | Year: 2012
The dynamics of light scattering attributes of minerogenic particles in the upper waters of an urban lake, Onondaga Lake, NY, U.S.A., are characterized for the spring-summer interval of 2010 with scanning electron microscopy interfaced with automated image and X-ray analyses (SAX). SAX results are used to estimate the minerogenic scattering coeffi cient (bm) through Mie theory calculations. Good optical closure of the summation of bm and organic particle scattering (bo), the latter estimated by empirical bio-optical models based on the concentration of chlorophyll-a, with paired bulk measurements of particulate scattering (bp) is demonstrated. The average of the ratio of (bm + bo) to bp was 1.07; the average percent difference between this summation and bp was 21 %. The contribution of bm to bp ranged fro m ~5 % during a dry weather interval to 70 % following a runoff event; the overall average, for the relatively low runoff study year, was nearly 25 %. Allochthonous clay mineral particles were the dominant minerogenic component, primarily responsible for the observed dynamics in bm. Calcium carbonate containing particles, with nuclei as clay minerals primarily and organic particles secondarily, were the second most important contributor to bm. Particles in the size range of 1-10 μm were responsible for bm during low tributary fl ow intervals, but particles > 10 μm became important following high runoff events. A strong inverse relationship between Secchi depth and bp prevailed, coupling this fundamental metric of water quality to the contributions of the various light scattering constituents. The light scattering and clarity conditions of the lake are considered in the context of prevailing and potential future driving conditions. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Peng F.,Upstate Freshwater Institute |
Effler S.W.,Upstate Freshwater Institute
Applied Optics | Year: 2012
The relationship between the particulate scattering coefficient (b p) and the concentration of suspended particulate matter (SPM), as represented by the mass-specific scattering coefficient of particulates (b *p bp/SPM), depends on particle size distribution (PSD). This dependence is quantified for minerogenic particle populations in this paper through calculations of b* p for common minerals as idealized populations (monodispersed spheres); contemporaneous measurements of bp, SPM, and light-scattering attributes of mineral particles with scanning electron microscopy interfaced with automated image and x-ray analyses (SAX), for a connected stream-reservoir system where minerogenic particles dominate b p; and estimates of bp and its size dependency (through SAX results-driven Mie theory calculations), particle volume concentration, and b*p . Modest changes in minerogenic PSDs are shown to result in substantial variations in b*p . Good closure of the SAX-based estimates of bp and particle volume concentration with bulk measurements is demonstrated. Converging relationships between b*p and particle size, developed from three approaches, were well described by power law expressions. © 2012 Optical Society of America.